Using a direct selective procedure which we have developed, we will isolate mutants deficient in NADP dependent glutamate dehydrogenase. We will use a variety of mutagens to induce these mutants in order to obtain a complete spectrum of mutational lesions at the locus. Particular emphasis will be placed on the use of mutagens such as nitrous acid and diepoxyoctane which have been shown to induce deletions. These mutations will be characterized by a variety of techniques including determination of CRM, reversion frequency complementation and response to nonsense suppressors. Utilizing these mutants we will construct a fine structure map of the locus by conventional techniques. A deletion map of the locus will also be constructed if a sufficient number of deletions are obtained.